Recently, with increasing integration densities of semiconductor devices, various photolithography techniques for forming fine patterns have been developed. Various metrology techniques have also been proposed to monitor a photolithographic process in order to manufacture highly-integrated devices. As integration densities of semiconductor devices increase, a critical dimension (CD) of a photoresist pattern decreases.
Examples of approaches to measuring focal variation generated in exposure equipment include focus exposure matrix (FEM), phase shift focus monitoring (PSFM), and phase grating focus monitoring (PGFM). In the FEM approach, a human evaluates a critical dimension (CD) of patterns and an image according to a constant variation of a focus and a dose for an exposure process by using scanning electron microscope (SEM) measuring equipment in order to determine a focal variation. Thus, the elapsed time from measurement to analysis can be excessive, and the analysis may be subjective. The PSFM and PGFM approaches both can use identical types of masks and identical measuring principles and methods.